Electrophoretic motion

A more detailed theory of electrophoresis is found in Refs. 9 and 58. The motion of the ions in the double layer due to the field F and due to the relative motion of the particle, cause a retardation of the electrophoretic motion that must be considered to... 

Theory of Electrophoretic Motion. The study of the mechanics of electrophoresis focuses on the basis of electric potential on the surface of an object, and the relation of the electric potential to the velocity of the particle. Whereas research has been generally limited to nonmolecular particles of weU-defined geometry and is not strictly apphcable to molecules such as proteins and DNA fragments, this work is useful for understanding the physics of electrophoretic motion. 

The influence of interionic fores on ion mobilities is twofold. The electrophoretic effect (occurring also in the case of the electrophoretic motion of charged colloidal particles in an electric field, cf. p. 242) is caused by the simultaneous movement of the ion in the direction of the applied... 

In closer approximations, correction must be made for conductivity effects (relaxation and electrophoretic) and for the real shape of the particles. Thus, the velocity of electrophoretic motion depends on the composition of the... 

Provided that fluid motion is uniform in the illuminated region of the suspension, then similar information may also be extracted by analysis of laser light scattering from particles undergoing electrophoretic motion, that is migratory motion in an electric field, superimposed on that motion. 

Ultramicroscopy is the preferred method for measuring the rate and/or extent of aggregation because it is direct. This method is also commonly used to observe the electrophoretic motions of colloidal species [81], as discussed in Section 4.3.1. 

During the past two decades, much attention has been drawn in this area and advances have been made in theoretical analysis concerning the applicability of Eq. (1) in a variety of systems. This chapter presents the state of understanding of the electrophoretic motion of colloidal particles under various conditions. We first introduce the basic concept and fundamental electrokinetic equations for electrophoretic motion. Then, we review some recent studies on the mobility of a single particle, the boundary effects and the particle interactions in electrophoresis. In addition, a few theoretical methods, which have been used to investigate the boundary effects and particle interactions, will be highlighted and demonstrated in the context. 

An analytical study using the method of reflections was conducted by Chen and Keh [9] to investigate the electrophoretic motion of two freely suspended nonconducting spherical particles with infinitely thin double layer. The particles may differ in size and zeta potential, and they are oriented arbitrarily with respect to the imposed electric field. The resulting translational and angular electrophoretic velocities are given by... 

When the gap width between two particles becomes very small, numerical calculations involved in both the bispherical coordinate method and the boundary collocation technique are computationally intensive because the number of terms in the series required to be retained to achieve a desired accuracy increases tremendously. To solve this near-contact motion more effectively and accurately, Loewenberg and Davis [43] developed a lubrication solution for the electrophoretic motion of two spherical particles in near contact along their line of centers with the assumption of infinitely thin ion cloud. The axisymmetric motion of the two particles in near contact can be approximated as the pairwise motion of the spheres in point contact plus a deviation stemming from their relative motion caused by the contact force. The lubrication results agree very well with those obtained from the collocation method. It is shown that near contact electrophoretic interparticle... 

Since an ion is subject to a resuitant or net force, its drift velocity also must be a net drift veiocity resolvable into components. Furthermore, since each component force shouid produce a component of the overaii drift velocity, there must be three components of the net drift veiocity. The first component, which will be designated v°, is the direct result of the externally applied field only and excludes the influence of interactions between the ion and the ionic cloud the second is the electrophoretic component Vg and arises from the participation of the ion in the electrophoretic motion of its cioud finaiiy, the third component is the reiaxation field component originating from the reiaxation force that retards the drift of the ion. Since the electrophoretic and reiaxation forces act in a sense opposite to the externally applied eiectric field, it follows that the electtophoretic and relaxation components must diminish the overall drift velocity (Fig. 4.91), i.e.,... 

In most electroosmotic flows in microchannels, the flow rates are very small (e.g., 0.1 pL/min.) and the size of the microchannels is very small (e.g., 10 100 jm), it is extremely difficult to measure directly the flow rate or velocity of the electroosmotic flow in microchannels. To study liquid flow in microchannels, various microflow visualization methods have evolved. Micro particle image velocimetry (microPIV) is a method that was adapted from well-developed PIV techniques for flows in macro-sized systems [18-22]. In the microPIV technique, the fluid motion is inferred from the motion of sub-micron tracer particles. To eliminate the effect of Brownian motion, temporal or spatial averaging must be employed. Particle affinities for other particles, channel walls, and free surfaces must also be considered. In electrokinetic flows, the electrophoretic motion of the tracer particles (relative to the bulk flow) is an additional consideration that must be taken. These are the disadvantages of the microPIV technique. 

Shear Plane Any species undergoing electrophoretic motion moves with a certain immobile part of the electric double layer that is commonly assumed to be distinguished from the mobile part by a sharp plane, the shear plane. The zeta potential is the potential at the shear plane. 

The movement of a charged colloidal particle in an external electrical field is called electrophoretic motion and the respective phenomenon is electrophoresis. The electrophoretic velocity in the two limiting cases, of a thin and thick EDL around a spherical particle, can be calculated by von Smoluchowski 3 and HiickeF formulas ... 

Fragmentation of zinc due to anomalous current distribution or a nonuniform cross section of dendritic stems and/or their fracturing during current reversal in the cathodic half-cycle. Electrophoretic motion of small fragments would then account for the shape change. 

We have not taken into consideration electrophoretic motion of polyions [35,39], However, we have already obtained characteristic features of the electric properties of polyelectrolytes in aqueous solution. Electric polarizability components originating from the fluctuations of condensed counterions show smaller concentration and salt dependence, while those due to a diffuse ion atmosphere, by contrast, a larger dependence. Anisotropy of the electrical polarizability Aa is positive without invoking an enhancement of the longitudinal component by the solvent flow. Simulation on the frequency dependence of the electrical polarizability is in progress to study how the... 

Churaev, Nikologorodskaya, and co-workers (33) investigated the Brownian and electrophoretic motion of silica hydrosol particles in aqueous solutions of an electrolyte at different concentrations of poly(ethylene oxide) (PEO) in the disperse medium. The adsorption isotherms of PEO on the surface of silica particles were obtained. The thickness of the adsorption layers of PEO was determined as a function of the electrolyte concentration and the pH of the dispersed medium. The results can be used in an analysis of the flocculation and stabilization conditions for colloidal dispersions of silica (with non-ionogenic water-soluble polymers of the PEO type). 

Figure 5. Effect of varying the shift. As the backshift is increased the far-field flux increases as does the length of the toe of the distribution. Once the shift passes the "flip point", the solute migrates opposite to the direction of its electrophoretic motion. See Table II for parameters used other than indicated in the figure.

The contribution of electrophoretic motion of particles into electric conductance of the disperse system, Xv, can be accounted for by introducing a term proportional to particle concentration, n ... 

The lag period before back diffusion starts is just like the whole diffusion time course it is practically identical for all the prepulse amplitudes. The lag period is also independent of the viscosity of the aqueous solution. It is possible that the photosystems aggregate when compressed under the influence of the electrical field, in which case the lag time could be identified with disaggregation time. Because contact between particles is a necessary condition for aggregation, elastic as well as electrostatic forces are probably invoked to stop electrophoretic motion. 

Electrophoresis The motion of colloidal species caused by an imposed electric field. The term replaces the older term cataphoresis. The species move with an electrophoretic velocity that depends on their electric charge and the electric field gradient. The electrophoretic mobility is the electrophoretic velocity per unit electric field gradient and is used to characterize specific systems. An older synonym, no longer in use, is kataphoresis. The term microelectrophoresis is sometimes used to indicate electrophoretic motion of a collection of particles on a small scale. Previously, microelectrophoresis was used to describe the measurement techniques in which electrophoretic mobilities are determined by observation through a microscope. The recommended term for these latter techniques is now microscopic electrophoresis (see reference 1). 

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